This invention relates to an improved process for preparing perfluoroalkane sulfonamides by reacting a perfluoroalkane sulfonylfluoride with an amine.
Perfluoroalkane sulfonamides are well known in the art. The primary use of such compounds resides mainly in the fact that they are important intermediate products in the preparation of surface-active substances.
Typically, perfluoroalkane sulfonamides are prepared by reacting perfluoroalkane sulfonylfluorides with amines. Thus, for example, U.S. Pat. No. 2,732,398 teaches the reaction of compounds such as perfluoro-n-octane sulfonylfluoride with piperidine or morpholine, whereby the corresponding sulfonamides are formed. However, in the reaction described therein, the yield of the desired product is relatively low and the product is very impure and difficult to purify.
In U.S. Pat. No. 2,759,019, in which the reaction of perfluoroalkane sulfonylfluorides with amines is also described, it is indicated that the crude reaction product which is in the form of an ethereal solution should be washed with water three times, after which, the ether layer is evaporated and the crude reaction product recrystallized twice from methyl cyclohexane. At a minimum, such complex recovery steps are burdensome, if not prohibative.
German Pat. No. 1,275,054, corresponding essentially to U.S. Pat. No. 3,458,571, also is concerned with the reaction of perfluoroalkane sulfonylfluorides with amines. The patent recommends mixing the reaction solution with an alcoholic solution of an inorganic base and processing the reaction product in a typical manner, after removal of the precipitated inorganic fluoride. Such a method is also very expensive and requires a time consuming purification process. It is also disadvantageous that, generally, a large excess of amine must be used. Furthermore, the purification is cumbersome and results in a product which is not as pure as is typically desirable. Finally, the process results in soluble fluorine compounds which may be environmentally harmful and there is no indication with respect to how the adverse environmental pollution might be counteracted.
With respect to the reactions described in all of the above patents, there is also a danger that the forming hydrofluoric acid may corrode the reaction vessels. As perfluoroalkane sulfonamides with a high degree of purity are required for various applications, there still exists a need for an improved preparation process which will particularly result in purer products and will not present any problems with respect to the disposal of hydrofluoric acid or other fluorine compounds. Furthermore, such a process which will not result in the corrosion of reaction vessels is especially desirable.
Thus, the primary purpose of this invention is to make available a process by means of which it is possible to prepare perfluoroalkane sulfonamides of satisfactory purity by reacting perfluoroalkane sulfonylfluorides with amines, resulting in a crude reaction product which can be converted, by relatively simple methods and without large expenditures, to a purer end product. Furthermore, the desired process should require only a small excess of amine in order to obtain an approximately quantitative conversion of the perfluoroalkane sulfonylfluoride. Additionally, the desired process should allow for the relatively simple removal of the hydrofluoric acid liberated during the reaction, without resulting in any problems such as environmental pollution while at the same time preventing corrosion of the reaction vessel, even if it is made of glass.